Iris

Generality

The iris is a thin membrane, of variable color and annular shape, visible from the front through the transparency of the cornea.

This ocular structure contains blood vessels, pigmented cells and two layers of smooth muscle. The contractions of these muscles allow the variation of the diameter of the pupil, the central opening of the iris.
In addition to determining the color of our eyes, in fact, the iris acts as a muscular diaphragm, regulating the amount of light that reaches the retina.